The present invention relates to an apparatus for determining the position of a switch and for monitoring the two-wire line connected to the switch for interruptions and short circuits. More particularly, the invention provides an evaluating apparatus which contains a generator for generating a test voltage or a test current having a periodically changing amplitude and which delivers at least one signal indicating the switch position and the presence of a disturbance on the line.
Known arrangements of this kind operate with an AC voltage or with alternating positive and negative square wave pulses as the test voltage and require, for determining the position of the switch, that the switch be designed as a double-throw switch and that a separate rectifier element be provided in each switch position current path. These rectifier elements are connected antiparallel, so that the evaluating device evaluates the direction of the current as the criterion for the switch position, and the states "current in both directions" or "no current" are the criteria for a line short circuit or for an interruption of the line (Publication "Siemens MDL-System", October 1974, pages 3, 4 and 5, and DE-AS No. 25 43 996). The use of a double-throw switch as the switch often means extra cost, since auxiliary switches provided for reporting purposes in switchgear and relays are as a rule designed as break contacts or make contacts.
It is an object of the present invention to provide an arrangement which permits, while using simple means, an indication of the switch position of a make or break contact as well as of a short circuit or an interruption in the line.